1. Field of the Invention
The present invention disclosed in the specification relates to a method of fabricating a thin film transistor using a crystalline semiconductor film.
2. Description of Related Art
Conventionally, there has been known a thin film transistor (hereinafter, referred to as TFT) using an amorphous silicon film. The transistor is utilized mainly for constituting an active matrix circuit of a liquid crystal display device of an active matrix type.
However, according to TFT using an amorphous silicon film, there poses a problem where the operational speed is retarded and a P-channel type one cannot be reduced to practice.
The transistor cannot be used in a liquid crystal display device of an active matrix type integrated with a peripheral drive circuit and various integrated circuits cannot be constituted by using such TFT because of such a problem.
There has been known a constitution using a crystalline silicon film as means for resolving the problem.
As methods of fabricating a crystalline silicon film, there are classified roughly into a method by heating and a method by irradiation of laser beam.
According to the method by heating, there poses a problem where a glass substrate cannot be utilized since a process at a high temperature as high as 900xc2x0 C. or higher is needed.
In consideration of the fact that a major field of application of TFT is a liquid crystal display device, capability of utilizing a glass substrate as a substrate constitutes a problem with priority.
Meanwhile, according to the method by irradiation of laser beam, although a process in which a substrate does not undergo thermal damage can be realized, the process is not satisfactory in view of uniformity and reproducibility of crystallinity and a degree of crystallinity of the semiconductor film.
As a means for resolving such a problem, there has been a method of accelerating crystallization by using a predetermined catalyst element which is the invention of the applicant.
According to the method, a catalyst element represented by nickel is introduced into an amorphous silicon film and a crystalline silicon film is provided later by a heating treatment.
According to the method, a crystalline silicon film having excellent crystallinity can be provided by a heating treatment at about 600xc2x0 C. or lower in which a glass substrate can be utilized.
However, nickel element remains in the crystalline silicon film by which adverse influence is effected on properties of TFT fabricated thereby.
Specifically, there poses a problem of aging change of the properties, deterioration in reliability or the like.
It is an object of the present invention disclosed in the specification to provide a technology in which in respect of TFT fabricated by using a crystalline semiconductor film obtained by utilizing a catalyst element promoting crystallization of semiconductor, adverse influence of the catalyst element is prevented from effecting on properties of TFT.
According to one aspect of the present invention disclosed in the specification, there is provided a method of fabricating a semiconductor device comprising the steps of making crystals grow from a region at a portion of an amorphous silicon film to other region thereof, the crystals growing in accordance with movement of a catalyst element promoting crystallization of semiconductor, making the catalyst element diffuse from the region of the portion of the amorphous silicon film, and gettering the catalyst element at the other region.
According to another aspect of the present invention, there is provided a method of fabricating a semiconductor device comprising the steps of making crystals grow from a region of a portion of an amorphous silicon film to other region thereof, the crystals growing in accordance with movement of a catalyst element promoting crystallization of semiconductor, and making the catalyst element diffuse from the region of the portion of the amorphous silicon film and gettering the catalyst element at the other region simultaneously.
According to another aspect of the present invention, there is provided a method of fabricating a semiconductor device comprising the steps of making crystals grow from a region of a portion of an amorphous silicon film to other region thereof, the crystals growing in accordance with movement of a catalyst element promoting crystallization of semiconductor, an origin of the movement of the catalyst element is formed at the region of the portion of the amorphous silicon film, and a destination of the movement of the catalyst element is formed at the other region.
It is most preferable to use Ni as the catalyst element in the aspects of the present invention.
According to another aspect of the present invention, one or a plurality selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Au, Ge, Pb and In can be used as the catalyst element.
In respect of the aspects of the present invention; the catalyst element is selectively added to or held in contact with the region of the portion of amorphous silicon film, and an element selected from the group consisting of P, As and Sb is selectively added to or held in contact with the other region.
An element selected from P, As and Sb is an element for gettering the catalyst element. As other element for gettering, N can be pointed out. In this signification, as an element for gettering, an element selected from elements of 15 group can be used.
According to the present invention disclosed in the specification, the highest effect can be achieved when nickel is selected as the catalyst element and P (phosphorus) is selected as the element for gettering.
As a method of introducing a catalyst element for promoting crystallization or a method of introducing an element for gettering, there can be used an ion implantation process, a diffusion process using a solution, a diffusion process using a solid, a process of diffusing the element from a film formed by a sputtering process or a CVD (Chemical Vapor Deposition) process, a plasma process, a gas adsorption process and so on.
Further, combination of these processes may be used. A selection of the processes may be carried out. For example, introduction of a catalyst element may be carried out by a process of using a solution, introduction of an element for gettering may be carried out by using a process by diffusion or the like.